The present invention relates to an oxygen scavenger, and more particularly to an oxygen scavenger which can effectively remove dissolved oxygen in water and, in particular, is useful in inhibiting the corrosion in a boiler system by removing dissolved oxygen in feed water. In addition, the present invention relates to boiler water treatment chemical including such an oxygen scavenger and descaling chemicals.
Dissolved oxygen in feed water contributes corrosion in components of a boiler system, such as a boiler main body, a heat exchanger and an economizer arranged in an upstream of the boiler main body, and a steam and condensate piping arranged in a downstream of the boiler main body. To inhibit the corrosion in the boiler system, dissolved oxygen in feed water should be removed by deoxidizing treatment of the feed water of the boiler.
Conventionally, chemical treatment or physical treatment has been applied for the removal of dissolved oxygen. As for the chemical treatment, a method of adding an oxygen scavenger such as hydrazine (N2H4), sodium sulfite (N2SO3), hydroxylamine group, or saccharide into the boiler water has been widely employed. Proposed in JPB S59-42073 and JPA H6-23394 is an agent containing hydroxylamine group and neutral amine.
However, the safety for humans of hydrazine is doubtful and thus the handling of hydrazine is at stake.
Since the reaction between sodium sulfite and oxygen is too rapid, sodium sulfite dissolved in water and stored in a tank reacts with oxygen in air before it is added in feed water, thereby reducing the concentration of effective component thereof. Therefore, there is a problem that sodium sulfite sometimes does not produce sufficient effect of dissolved oxygen removal. Since the feed water treated with sodium sulfite contains sulphate ion as a reaction product of the sodium sulfite and oxygen, there is another problem that the corrosion and scale in a boiler system are easily caused.
There is also a problem that hydroxylamine group generates acid such as nitric acid when the hydroxylamine group is added in feed water and reacts with oxygen in the boiler, thereby reducing corrosion inhibition effect for the boiler main body.
Saccharide has disadvantages in that it is difficult to measure the residual concentration in boiler water and thus difficult to control the right amount to be added, and saccharide gives odor to the steam.
Using azo compound as an oxygen scavenger has been already proposed. For example, 2,2-azobis(N,Nxe2x80x2-dimethlene isobuthy amidine)2,2-azobis(isobuthyl amide).2 hydrate, 4,4-azobis(4-cyano caproic acid), and 2,2-azobis(2-amidino propane).HCl have been proposed.
Each of these azo compounds provides high efficiency of dissolved oxygen removal. However, azo compounds have disadvantages in producing various organic matters such as formic acid and acetic acid in a boiler drum and the steam and thereby adversely affecting the steam quality and the steam purity.
It is the first object of the present invention to provide a novel oxygen scavenger which can efficiently remove dissolve oxygen in boiler feed water while providing high safety for humans.
It is the second object of the present invention to provide an oxygen scavenger having a heterocyclic compound with N-substituted amino group as an effective component which can adequately exhibit the deoxidization effect not only for feed water lines, a boiler main body, or steam and condensate lines for high temperature water, but also for feed water lines for low temperature water.
It is the third object of the present invention to provide a novel chemical for treating boiler water which can exhibit corrosion inhibition effect to both a boiler main body and a piping for the steam and condensate.
It is the fourth object of the present invention to provide a boiler water treatment chemical which has high corrosion inhibition effect by a heterocyclic compound with N-substituted amino group and exhibit excellent corrosion inhibition effect and scale inhibition effect as a state of a solution which contains component agents.
In an oxygen scavenger of a first aspect. the effective component thereof consists essentially of a heterocyclic compound having Nxe2x80x94N bond in a ring thereof
In an oxygen scavenger of a second aspect. the effective component thereof consists of a heterocyclic compound having N-substituted amino group or its water soluble salt.
In an oxygen scavenger of a third aspect. the effective component thereof consists of the following heterocyclic compound: 
(wherein a, b are integers between 0 and 5 to satisfy a relation xe2x80x9c2xe2x89xa6a+bxe2x89xa65xe2x80x9d).
In an oxygen scavenger of a fourth aspect. the effective component thereof consists essentially of a heterocyclic compound represented by the following formula: 
(wherein R1, R2, R3, R4 may be the same or different from each other and each designates any one of hydrogen, lower alkyl group having 1-8 carbon atoms, and aryl group also having 1-8 carbon atoms, and X designates any one of hydrogen, amino group, alkyl group or dialkylamino group having 1-8 carbon atoms, and lower alkyl group or aryl group having 1-8 carbon atoms).
In an oxygen scavenger of a fifth aspect. the effective component thereof consists essentially of azodicarbonamide.
The oxygen scavengers of the first through fifth aspect may be prepared by combining two or more kinds of components.
The amount of the effective component of each aspect is not limited and can be altered to suitably correspond to the concentration of dissolved oxygen in water as a subject. Normally, the amount is, however, between 0.001 and 1000 mg, preferably between 1 and 300 mg relative to 1 lit. of feed water.
An oxygen scavenger of a sixth aspect includes a heterocyclic compound with N-substituted amino group, or the salt thereof, and a hydroxybenzene derivative.
In the oxygen scavenger of the sixth aspect, because of the catalysis of the hydroxybenzene derivative, the heterocyclic compound with N-substituted amino group or the salt thereof can exhibit the excellent deoxidization effect even in feed water lines for low temperature water.
A seventh aspect provides a chemical for treating boiler water including a heterocyclic compound with N-substituted amino group and neutral amine.
An eighth aspect provides a boiler water treatment chemical including a heterocyclic compound with N-substituted amino group, or the salt thereof, and alkaline agent and/or water soluble polymer.